Blood in your urine can come from anywhere along your urinary tract, from your kidneys down to your urethra. The causes range from completely harmless to serious, and the color and timing of the bleeding often hint at what’s going on. Sometimes the blood is visible, turning your urine pink, red, or cola-colored. Other times it’s only detectable under a microscope during a routine urine test, defined as three or more red blood cells per high-powered field on a single sample.
Urinary Tract Infections
UTIs are one of the most common reasons people notice blood in their urine, especially women. Bacteria enter the urethra and multiply in the bladder, triggering inflammation that irritates the bladder lining and causes it to bleed. The blood is usually accompanied by other hard-to-miss symptoms: burning during urination, a constant urge to go, cloudy or strong-smelling urine, and pelvic pressure. Kidney infections can also cause bloody urine, often alongside back pain, fever, and chills. UTIs are typically straightforward to treat, and the bleeding resolves once the infection clears.
Kidney Stones
Kidney stones cause blood through mechanical erosion. As a stone moves through the urinary tract, its rough edges scrape against the soft mucosal lining of the ureter or bladder, breaking tiny blood vessels along the way. The bleeding can be visible or microscopic, and it often comes with intense, wave-like pain in the side or lower back that radiates toward the groin. Small stones may pass on their own over days to weeks. Larger ones sometimes require procedures to break them up or remove them. If you’ve had one kidney stone, your lifetime risk of another is significant, so identifying the stone type helps guide prevention through dietary changes or increased fluid intake.
Enlarged Prostate
In men, an enlarged prostate is a common benign cause of blood in the urine, particularly after age 50. As the prostate grows, it creates irregular nodular tissue that pushes into the urethra, narrowing the channel urine flows through. This forces urine into turbulent flow patterns that increase pressure on nearby blood vessels. The surface of the enlarged tissue is also fragile and bleeds easily, partly because the tissue develops a higher density of small blood vessels with thinner walls and less supportive smooth muscle. The bleeding may come and go and is sometimes triggered by straining to urinate.
Vigorous Exercise
Strenuous physical activity can cause blood in the urine even in perfectly healthy people. This is sometimes called “runner’s hematuria,” though it’s not limited to running. Long-distance running, cycling, rowing, and other intense endurance activities are the most common triggers. The exact mechanism isn’t fully understood, but it likely involves a combination of repeated bladder impact, reduced blood flow to the kidneys during exertion, and breakdown of red blood cells. The key feature of exercise-induced hematuria is that it resolves with rest, typically within 24 to 72 hours. If it doesn’t clear up after a few days of rest, something else is going on.
Bladder and Kidney Cancer
Painless blood in the urine, especially in someone over 55, is the symptom that raises the most concern. Bladder cancer is the most common urinary tract malignancy, and visible blood in the urine is often its first and only sign. Kidney cancer can present the same way. Several risk factors increase the likelihood that bloody urine is cancer-related:
- Smoking. Your body filters the harmful chemicals from tobacco smoke through the kidneys and into the bladder, where they sit in contact with the bladder lining. This repeated chemical exposure damages cells over time and is the single biggest modifiable risk factor for bladder cancer.
- Age. Most people diagnosed with bladder cancer are older than 55. Risk climbs steadily with age.
- Occupational chemical exposure. Workers in industries that involve dyes, rubber, leather, textiles, and paint products face higher risk. Arsenic exposure is also linked to bladder cancer. The kidneys filter these chemicals from the bloodstream and concentrate them in the bladder.
Painless hematuria doesn’t mean cancer is likely, but it does mean the possibility should be ruled out, particularly if you have any of these risk factors.
Kidney Disease
Diseases that damage the kidney’s filtering units can leak red blood cells into the urine. This includes conditions like glomerulonephritis, where the tiny filters in the kidney become inflamed, often as part of an immune response. IgA nephropathy, one of the most common forms, sometimes causes visible blood in the urine during or shortly after a cold or respiratory infection. Inherited conditions like polycystic kidney disease, where fluid-filled cysts grow in the kidneys over time, can also cause bleeding. Kidney-related causes of hematuria often show up alongside protein in the urine, high blood pressure, or changes in kidney function on blood tests.
Medications and Blood Thinners
Blood-thinning medications, including both prescription anticoagulants and common over-the-counter options like aspirin, can make you more prone to urinary bleeding. They don’t cause hematuria on their own in a healthy urinary tract, but they can unmask bleeding from an underlying condition that might otherwise go unnoticed. If you notice blood in your urine while taking a blood thinner, the medication may be amplifying the problem, but there’s still an underlying source worth identifying.
When It’s Not Actually Blood
Not all red or pink urine contains blood. Beets, blackberries, and rhubarb can turn urine red or pink, a harmless phenomenon sometimes called “beeturia.” Several medications also change urine color in ways that mimic blood. A tuberculosis drug called rifampin turns urine reddish-orange. Phenazopyridine, a common over-the-counter medication for urinary tract pain, turns it bright orange. Laxatives containing senna can produce similar color changes. If your urine looks unusual but you recently ate one of these foods or started a new medication, that’s the most likely explanation. A simple urinalysis confirms whether actual red blood cells are present.
What to Expect During Evaluation
The first step is always a urinalysis, which confirms whether red blood cells are actually present and can also detect signs of infection or protein that might point toward a kidney problem. If blood is confirmed, the evaluation typically branches based on your age, sex, symptoms, and risk factors.
Imaging, often a CT scan of the urinary tract, lets doctors look for kidney stones, tumors, structural abnormalities, or other sources of bleeding in the kidneys and ureters. Cystoscopy, where a thin camera is passed through the urethra into the bladder, gives a direct view of the bladder lining and is the most reliable way to detect or rule out bladder cancer. It’s a quick outpatient procedure, usually done with local numbing gel, and takes only a few minutes.
Visible blood in the urine almost always prompts a full workup. Microscopic hematuria found incidentally on a routine test is evaluated more selectively. A single episode in a young person with an obvious explanation, like a UTI or intense exercise, may just need a follow-up urinalysis to confirm it has resolved. Persistent microscopic hematuria, especially in older adults or smokers, gets a more thorough investigation.